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Controllers
Basically I converted my system to an automatic recirculating heat exchange system. Here's a look at the temperature controlled setup. I picked up two Extech (48VTR-13) PID Controllers on eBay for about $100 a piece. I got some Solid State Relays on eBay also. In very generic terms the PID is a "fancy" thermostat or temperature controller. It has many other features that at this time, I'm not using. Basically I use one to control the Hot Liquor Tank (HLT) and the other controls the the temperature of the grain in the Mash Lauter Tun (MLT).
Here's a drawing of the HLT Controller, it works like this. I set the desired temperature on the PID, let's say 135°F (this is the "Set Value" or "SV"). The PID gets a reading from a thermocouple (temperature sensor) and displays it as the "Process Value" or "PV". If the PV is less than the SV the PID sends a signal to a Solid State Relay (SSR) which turns on the power to a heating element in the HLT. This heats the water. When the water gets to 135°F the signal to the SSR is switched off, which in turn switches off the power to the heating element.
This is a drawing of the MLT Controller. It works pretty much the same as the HLT Controller, except that instead of heating elements, it controls Solenoid Valves. I start the pump to recirculate the wort in the MLT. If the wort needs to be heated Valve 1 opens and Valve 2 closes. This directs the wort through the copper heating coil (which runs through the HLT), the wort is heated and returns to the MLT. When the desired temperature is reached Valve 1 closes and Valve 2 opens. This bypasses the heating coil and returns the wort directly back to the MLT. I take a temperature reading on the outlet of the MLT, this temperature ends up being pretty close to the actual temperature of the grain bed. Solenoid valves are pretty expensive. They can run from $50 to well over $100, depending on what they're made of. I ended up using a water inlet valve for a washing machine. (It's what you connect the hot and cold water hoses to) The picture shows it from the front, the back is covered with a grey plastic outlet box to protect the electrical connections. I got it new for $22 at a local appliance parts store. It actually is two valves in one. So it has two inputs and one output, seems to meet my needs so far.
The controllers are housed in plastic project boxes I got at Radio Shack. The Solid State Relays need to be mounted on heat sinks to operate properly. They can be seen under the project boxes in this picture. They are actually mounted to the outside of the boxes and the SSR's are mounted to them through a square hole in the bottom of the box. There just wasn't enough room to put everything inside the box. This actually worked out well because it allowed for better heat dissipation. This is a look at the inside of the MLT Controller. Another thought I had was to make these controllers multi-purpose. I have previously used the HLT controller to maintain the temperature in my beer fridge. The PID has the option to act as a heating control or a cooling control. I think I'll also use one of them to control my electric smoker, which currently has no temperature control at all and always gets too hot.
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